The invention relates to a clamping according to the pre-characterizing clause of claim 1.
A clamping chuck of this type is known from German utility model 90 00 245.8. The known clamping chuck possesses a clamping portion, by means of which the clamping chuck can be clamped into an electric screwdriver or the like. The shank forming this clamping portion at one end possesses, at the other end, a toolholder for accommodating a screwdriver insert or the like. In the prior art, it is known, furthermore, to provide screwdriver inserts with a torsional portion, in order to absorb torsion peaks when a screw is being screwed in. The maximum torque in the peaks is thereby to be absorbed. The torque peaks are reduced and smoothed.
The object on which the invention is based is, therefore, to improve a clamping chuck of this type in functional terms.
According to the invention, the torsional portion is associated with the clamping chuck. What is ensured at the same time is that elastic twistability takes place only over a predetermined angular range, so as to prevent damage to the torsion member. The torsion member preferably couples two shank portions located axially one behind the other. These shank portions can be rotated relative to one another until a limiting torque is reached. Stops are provided, which are spaced from one another by a gap. The shank portions consist preferably of sleeve portions located one behind the other. The two ends of the preferably dumbbell-shaped torsion member fit positively in the cavities of these sleeve portions. In a first variant of the invention, the stops may be formed by the two sleeve-shaped shank portions. Preferably, these stops are formed by sleeve edge portions of the shank portions, the said sleeve edge portions engaging with movement play one in the other. The torsion portion of the torsion member is preferably cylindrical. Furthermore, a cuff may be provided, which spans the connecting joint between the two shank portions. The cuff ensures that the two shank portions are restrained in the axial direction, but allows rotatability of the two shank portions relative to one another, the angular amount of rotatability being determined by the gap width between the two stops. In a further variant of the invention, the two sleeve portions may likewise be rotated relative to one another until the limiting torque is reached. There, however, the stops are formed by a profile portion which directly adjoins the torsion zone and which engages undersized into a corresponding profiling of the sleeve surrounding the torsion portion, so that, as in the first exemplary embodiment, this sleeve is loaded with a torque only when the limiting torque is reached and the two profile portions have rotated relative to one another by a corresponding angular amount. In a preferred embodiment, the torsion portion is a materially integral prolongation of the clamping portion. The torsion portion may be prolonged in a materially integral manner into a securing portion, by means of which the core forming the clamping portion is connected fixedly in terms of rotation to a shank portion forming the toolholder. The two sleeve-like shank portions may butt one against the other so as to form a circumferential joint. This joint may have oblique end faces. The clamping chuck may be provided, furthermore, with an actuating sleeve which spans the cuff. As regards the functioning of the actuating sleeve and of the clamping means which is formed as a ball, reference is made to German utility model specification 90 00 245.3. The two sleeves are held by means of the torsion member in an angular position relative to one another such that elastic yieldability is possible both in the left-hand direction and in the right-hand direction. There is movement play on both sides. During the movement of the two sleeves relative to one another, the torsion member is twisted. Up to a first limiting torque, the clamping chuck behaves in the same way as a virtually rigid body. The first limiting torque is defined by the dimensioning and pre-treatment of the torsion portion of the torsion member. When the first limiting torque is exceeded, the torsion member gives way in a resiliently elastic manner, the torsion portion twisting until the two stops butt one against the other. Between the two limiting torques, the two shank, portions can be rotated relative to one another by the amount of the movement play. As soon as the stops butt one against the other, the clamping chuck acts once again as a virtually rigid body.